Laboratory Disk Grinder, Replacement Grinding Disk and Use of a Grinding Disk

ABSTRACT

The present disclosure relates to a laboratory wheel grinder and a method for plane grinding a lower side of specimens, in particular mounted specimens, as well as a replacement grinding disc for the laboratory wheel grinder and the use of a grinding disc in a laboratory wheel grinder, wherein the grinding disc is divided into a peripheral annular first surface and a central second surface arranged within the peripheral annular first surface wherein the upper surface of the carrier disc is covered with the abrasive only in the peripheral annular first surface so as to form a grinding peripheral annular first surface and a passive central second surface.

FIELD OF THE INVENTION

The invention relates to a laboratory-scale material-removing device for sanding specimens, in the form of a laboratory wheel grinder, a method for surface-grinding an underside of specimens, in particular mounted specimens or samples, and a replacement grinding disc for the laboratory wheel grinder and the use of a grinding disc in a laboratory wheel grinder.

BACKGROUND AND GENERAL DESCRIPTION OF THE INVENTION

In order to perform material tests on specimens in metallography, smaller specimen pieces are often mounted in a cylindrical body made from plastic material. The diameter of such mounted specimens or samples is, for example, 40 mm. Subsequently, such mounted specimens are surface-ground and, if necessary, polished in order to be able to perform tests on the material, for example hardness tests or microstructure analyses, on the surface of the material specimen. In order to grind the surface and, if necessary, polish of the mounted metallographic specimens, laboratory wheel grinders with a rotating grinding disc are typically used, for example those produced by ATM Qness GmbH under the brand names Saphir and Rubin, cf. www.qatm.com. Frequently, such laboratory wheel grinders are designed as combined grinding and polishing units, i.e. the laboratory wheel grinders can also be equipped with a polishing wheel to be able to offer an additional polishing function. Such laboratory wheel grinders are thus typically used for surface-grinding and, if necessary, polishing the underside of mounted specimens in materials tests, in particular hardness tests or a microstructure analysis.

Such laboratory wheel grinders are available either in a single-spindle or a multi-spindle version. Manual laboratory wheel grinders basically have a housing with a tray, a drive motor and a grinding plate. With these simple devices, the mounted specimen can be pressed down and ground by hand. Automatic grinders additionally feature a device head, sometimes called a polishing head, with a piston in which a rotating specimen holder can be mounted. The specimen can either lie loosely in the specimen holder and be pressed against the grinding plate by individual pressure pins (individual specimen pressure), or it is fixed in the specimen holder and the specimen holder as a whole is pressed against the grinding plate (central pressure).

The grinding discs for such laboratory wheel grinders typically feature a full-surface design, i.e. the abrasive with a specific grit and specific scatter is distributed across the entire surface of the grinding disc from the inside to the outside, following a specific pattern if necessary.

The peripheral speed of the grinding disc decreases towards the center, however. Due to the decreasing peripheral speed, the pressure on the specimen increases towards the center of the wheel. Typically, no work is done in the center of the wheel because the peripheral speed is zero and thus no material is removed. Therefore, primarily the outer region of the wheel is used, and the inner region is not used. After prolonged use, this leads to varying degrees of wear, so that the grinding disc is no longer flat after prolonged use, which in turn can have a negative effect on the generally desired flatness of the specimen.

These negative effects are counteracted by regularly whetting the grinding disc with a grinding stone, typically by hand, which, however, leads to additional effort in a disadvantageous manner. Moreover, this wastes abrasive material, which leads to unnecessary costs.

These effects are even more problematic in automatic laboratory wheel grinders, in which one or more specimens are mounted in a specimen holder that is automatically pressed against the grinding disc by means of a piston rotatably mounted on a device head or grinding and polishing head. In this case, the specimens are typically always ground on the same radius of the grinding disc, which leads in particular to an uneven wear of the abrasive on the grinding disc, namely in an outer annular region in which the specimen or specimens are primarily ground. Since the specimen, or in the case of a plurality of specimens, the totality of the specimens always remain approximately in the same radial radius interval despite the self-rotation, a difference in height of the grinding surface, i.e. of the grinding product between the radially outer region and the central region of the grinding disc can occur during longer-term use, since the wear in the central region is less or there is no wear at all.

If such an unevenly worn grinding disc is not regularly whetted with a grindstone, actual ridges will start to form on the abrasive at a certain radius, which can lead to a basically undesirable rounding of the lower outer edge of the mounted specimen.

It is therefore an object of the present invention to provide a laboratory wheel grinder, a method, a replacement grinding disc, and a use of a grinding disc that avoid or at least mitigate the disadvantages described above.

A further aspect of the object of the present invention is to provide a laboratory wheel grinder, a method, a replacement grinding disc and a use of a grinding disc, in which, on the one hand, the need to remove the grinding disc is eliminated or at least reduced and in which, this notwithstanding, the underside of the ground mounted specimens has a high degree of flatness, due to which, in particular, a rounding at the edge of the specimen is avoided or at least reduced, while, at the same time, the grinding disc has a long service life.

The object of the invention is achieved by the subject matter of the independent claims. Preferred embodiments are the subject matter of the dependent claims.

The invention relates to a laboratory-scale wheel grinder or plate grinder with a rotating grinding wheel or grinding disc for grinding the surface of an underside of, in particular, mounted metallographic specimens, wherein the laboratory wheel grinder can also be designed as a combined grinding and polishing device. It comprises a device housing with a grinding disc mounting plate and a drive motor by means of which the grinding disc mounting plate is set in rotation. The rotation speed of the grinding disc is preferably adjustable and can be adjusted, for example, between 30 rpm and 600 rpm.

A grinding disc, in particular a thin grinding disc, can be attached, e.g. affixed or adhered, to the grinding disc mounting plate, which substantially consists of a carrier wheel or carrier disc and an abrasive layer in the form of abrasive grit or abrasive particles bonded to the carrier disc as an abrasive. The abrasive grit is preferably bonded by means of a synthetic resin bond or a metal bond, for example a nickel bond, in which the abrasive grit is mounted.

The carrier disc of the grinding disc has an upper side and a lower side and is detachably attached, for example adhesively, to the grinding disc mounting plate with the lower side in order to make it possible to easily replace the grinding disc as consumable material after a corresponding wear or in order to grind with a different grit size. For this purpose, the grinding disc can be adhered, for example magnetically, to the grinding disc mounting plate, i.e. by means of a magnetic adhesion of the carrier disc to the grinding disc mounting plate or by means of a carrier disc with an adhesive underside, for example with a gel-like surface coating. The grinding disc is, in particular, considerably larger than the specimen to be ground flat, the diameter of which typically ranges from 30 mm to 60 mm.

According to one aspect of the invention, the grinding disc is divided into a peripheral annular first surface and a central second surface arranged within the peripheral annular first surface, wherein the upper surface of the carrier disc is fully covered with the abrasive grit as abrasive material only in the peripheral annular first surface, so that a grinding peripheral annular first surface and a passive, non-abrasive central second surface are formed. In other words, the grinding disc has a grinding peripheral annular region covered by abrasive material and a free space in the annular inner region in which the abrasive material was not applied, i.e. the carrier disc of the grinding disc is present in the passive non-abrasive central second region but is substantially not covered by abrasive grit as abrasive material. Alternatively, it is also conceivable to omit the grinding disc mounting plate and the carrier disc in the non-abrasive central second surface and to provide a drain for the coolant in the grinding disc mounting plate. The abrasive layer on the carrier disc, i.e. the actively grinding surface of the grinding disc is thus formed as an annular surface and surrounds a bare non-grinding central region of the carrier disc. The abrasive layer is thus annular in shape with a free space in the center around the axis of rotation of the grinding disc.

The radial width of the grinding peripheral annular region or the radial width of the annular abrasive layer is preferably adapted to the size of the specimen or specimens in such a way that the edge region of the specimen or specimens exceeds the grinding peripheral annular region, in particular permanently or at least regularly, in the radially inward direction, so that no surfaces remain in the central region of the grinding disc which do not, in particular permanently or at least regularly, contribute to the grinding of the specimen or specimens. In other words, the entire surface of the abrasive layer grinds the lower side of the abrasive(s) without having regions of the abrasive layer that are not covered by the specimen(s). In other words, the diameter of the non-abrasive central second surface is large enough that the specimen(s) permanently or at least regularly exceed the passive non-abrasive central second surface in the radially inward direction. Thus, a differing wear of the abrasive or the abrasive layer can be avoided in an advantageous manner, especially in the central inner region of the grinding disc, since there is preferably no abrasive there at all.

This way, a synergistic double benefit can be achieved. On the one hand, regularly dressing of the grinding disc can be eliminated or can at least be significantly reduced, while a flat grinding result for the lower side of the specimen or specimens is still ensured, even if the grinding disc has already reached a certain degree of wear. On the other hand, wasting of abrasive material can be avoided or at least reduced at points where the peripheral speed of the grinding disc is anyway too low to achieve an optimum grinding result.

Preferably, uneven wear of the abrasive can additionally be avoided on the radial outer side of the grinding disc as well by having specimen or specimens also exceed the grinding peripheral annular region in the radially outward direction, i.e. projecting or extending radially outward beyond the grinding peripheral annular region.

In the grinding peripheral annular region or the ring-shaped abrasive layer, the abrasive grit is bonded to the carrier disc as abrasives with a specific grit size and specific dispersion by means of a binding agent. Epoxy resin or nickel, for example, can be used as the bonding agent. Industrially produced diamond in the form of diamond particles with the desired grit size is used as the abrasive, for example, the diamond particles being bonded in synthetic resin with a desired hardness (soft, medium, hard). Preferably, the abrasive particles are printed as a powder, e.g. a diamond powder, in a printing process with the synthetic resin on the surface of the carrier disc and thus locally bonded. Accordingly, the abrasive grit is preferably printed onto the grinding peripheral annular first surface with bonding agents in a predefined pattern. The screen-printing process is particularly suitable for this purpose. Alternatively, the abrasive particles can also be bonded to the carrier disc by means of a metal bond, e.g. a nickel bond.

As a result, a surface of the annular abrasive layer is formed in the cross section of the grinding disc by the abrasive grit mounted in the bonding agent defining a common annular abrasive first surface of the grinding disc in the grinding peripheral annular first surface. The carrier disc of the grinding disc forms a central non-abrasive second surface of the grinding disc in the passive non-abrasive central second surface, because the central second surface of the carrier disc is not covered with abrasive grit, or because there is no abrasive layer in that region. Thus, when the grinding disc is in a fresh unused condition, the common annular abrasive first surface of the grinding disc is higher than the central non-abrasive second surface of the grinding disc, so that a height difference or step is formed at the inner radius of the annular abrasive layer between the common annular abrasive first surface and the central non-abrasive second surface, and the specimen or specimens move toward the passive non-abrasive central second surface, where they are axially spaced from the grinding disc due to the height difference.

The difference in height of the step between the common annular abrasive first surface or the surface of the annular abrasive layer and the central non-abrasive second surface or the thickness of the abrasive layer can be, for example, between 50 μm and 5 mm, preferably between 100 μm and 3 mm, preferably between 200 μm and 1.5 mm, depending on the grinding disc. Suitable grit sizes for the grinding peripheral annular first surface have grit sizes of 3 μm, 6 μm, 15 μm, 30 μm, 60 μm, 125 μm or 250 μm, or grit sizes of 80, 120, 180, 240, 320, 600, 800, 1000, 1200, 2500, with the grit size corresponding to 25.4 mm (1 inch)/grit. For a 1000 grit, for example, the grit size is 25.4 mm/1000=0.025 mm or for an 80 grit, 25.4 mm/80=0.32 mm. Grit sizes below 80 are rather uncommon for laboratory wheel grinders, so the largest grit size is preferably about 0.32 mm or 0.25 mm.

The abrasive grit is bonded in the grinding peripheral annular first surface with the bonding agent on the upper surface of the carrier disc, preferably in multiple layers, preferably in 3 to 200 layers, preferably in 5 to 100 layers, so that on average about 3 to 200, preferably about 5 to 100 abrasive particles are bonded axially one above the other in the multilayer abrasive layer.

Preferably, the multilayer abrasive layer is self-sharpening, e.g. in such a way that dull abrasive grit, for example diamond particles, break out during the grinding process and fresh abrasive grit, e.g. diamond particles, emerge from an underlying layer to the surface.

On the one hand, this has the advantage that the grinding disc in the laboratory wheel grinder has a long service life and that a large number of mounted specimens or mounted samples can be ground in succession before the grinding disc has to be replaced. On the other hand, in particular a combination of such a grinding disc with a plurality of layers of abrasive grit bonded one on top of the other, which is successively removed, and the lack of an abrasive layer in the inner region of the grinding disc provides for a synergistic advantage, since, without the present invention, in particular in the case of multi-layer self-sharpening grinding discs, the resulting difference in height is particularly large due to the greatly varying wear.

In other words, the difference in height between the grinding peripheral annular first surface and the passive, non-grinding central second surface preferably does not correspond to the size of the abrasive grit, but is considerably greater than the size of the abrasive grit, since the bond, preferably a synthetic resin bond with diamond particles, is applied in several layers, e.g. by means of a screen-printing process, and thus height differences of for example up to 1 mm can be applied even for smaller grit sizes. This considerably increases the service life of the grinding disc, even if the abrasive grit becomes dull relatively quickly. As already explained above, abrasive grit breaks off with the bedding when dull due to the high cutting force and the fresh and still sharp abrasive grit underneath emerges to the surface and develop their grinding effect, if the abrasive grit is bonded in multiple layers. A long service life can be achieved as a result.

The grinding disc is preferably (circular) round and/or has an outer diameter of between 100 mm and 500 mm, preferably of between 150 mm and 400 mm, preferably of 300 mm+/−50 mm.

The grinding peripheral annular first surface or the annular abrasive layer preferably has an inner diameter D_i and an outer diameter D_a, with half of the difference between the inner diameter D_i and the outer diameter D_a, defining the radial width B_r of the annular abrasive layer and being between 240 mm and 20 mm, preferably between 180 mm and 25 mm, preferably 30 mm+/−10 mm or 125 mm +/−50 mm. For grinding an individual specimen, the radial width B_r of the annular abrasive layer can be 30 mm+/−10 mm or between 5% and 50% narrower than the diameter of the mounted specimen, and for a specimen holder with a plurality of specimens, the radial width B_r of the annular abrasive layer can be 125 mm+/−50 mm or between 150% and 400% of the diameter of an individual mounted specimen.

According to a preferred embodiment, the grinding peripheral annular first surface or the annular abrasive layer has an inner diameter D_i and an outer diameter D_a, the inner diameter D_i corresponding to the outer diameter of the passive non-abrasive central second surface and the inner diameter D_i preferably being between 20 mm and 450 mm, preferably between 30 mm and 300 mm, preferably 50 mm+/−30 mm for a specimen holder with a plurality of specimen or 250 mm+/−50 mm for an individual specimen and/or the outer diameter D_a preferably being between 100 mm and 500 mm, preferably between 150 mm and 400 mm, preferably in the range of 300 mm+/−50 mm.

The carrier disc is preferably designed as a sheet, in particular a stiff sheet. A sufficient rigidity of the carrier disc is advantageous for the grinding parameters that are important for a laboratory wheel grinder. The sheet metal is preferably a metal sheet, but it can also be a plastic sheet. Preferably, the thickness of the sheet is between 0.1 mm and 3 mm. A metal sheet with a thickness of 0.5 mm is suitable, for example. Particularly suitable are magnetizable metal sheets, e.g. magnetizable steel sheets, because these can be directly magnetically attached to the grinding disc mounting plate if the grinding disc mounting plate contains magnets.

The abrasive grit is preferably made up of diamond particles, which in turn has a positive effect on the service life of the grinding disc.

The abrasive grit is preferably bonded to the carrier disc by means of a synthetic resin bond. Alternatively, a nickel bond can be considered. The abrasive grit is mounted in the bonding agent. The bond is created, for example, by means of a screen-printing process.

The abrasive grit or diamond particles can even be bonded directly to the sheet with the bonding agent. Alternatively, the grinding disc may comprise a textile intermediate layer to which the abrasive grit or diamond particles are bonded with the bonding agent. The latter can have advantages in terms of production technology. In this case, the textile backing forms a flexible grinding pad with the abrasive layer, which is then in turn bonded to the sheet, so that the sheet together with the textile intermediate layer forms the carrier disc in order to obtain a stiff grinding disc.

According to a preferred embodiment, the grinding disc has adhesive means with which the grinding disc is adhered with its lower side to the grinding disc mounting plate in such a way that it can be peeled off. The adhesion can be achieved, for example, by means of a magnetic force or a gel-like adhesive layer. This allows the grinding disc to be easily and conveniently replaced by the user, e.g. in order to change the grit size or when the grinding disc has reached the end of its service life.

Preferably, the grinding disc mounting plate and thus the grinding disc rotates in a tray which collects the grinding abrasion and, if necessary, cooling liquid. This makes it possible to cool the grinding disc with cooling liquid, e.g. water, and the grinding abrasion to be flushed away.

According to a preferred embodiment, the laboratory wheel grinder has a preferably exchangeable specimen holder, which can be designed, for example, as a plate for inserting a plurality of specimens or as a gripper for an individual specimen, wherein the specimen or specimens are inserted into the specimen holder and are each pressed against the grinding disc by means of the specimen holder by an individual contact pressure or by a central contact pressure. In the case of an individual contact pressure, the specimen or specimens are merely inserted into the specimen holder, and in the case of a central contact pressure, they are firmly clamped in place. Furthermore, in addition to the rotation of the grinding disc, the specimen holder rotates with the inserted specimen or specimens during the grinding process, and during the opposite or same-direction double rotation of the grinding disc and the specimen holder, an edge region of the specimen or specimens protrudes in the radially inside direction and, if necessary, additionally outside over the grinding peripheral annular first surface or annular abrasive layer and radially inside into the passive, non-grinding central second surface. This ensures that there is no abrasive in the central inner region of the grinding disc that is not uniformly worn by the specimen or the specimens.

In other words, i) in the case of an individual specimen, the specimen defines an outer diameter and the specimen protrudes radially inward during the grinding process with its outer diameter and, if necessary, outward beyond the grinding peripheral annular first surface or the annular abrasive layer, respectively; and ii) in the case of a specimen holder with a plurality of specimens inserted, the totality of the specimens defines a total outer diameter with respect to the rotation of the specimen holder and the total outer diameter projects radially inward and optionally outward during the grinding operation beyond the grinding peripheral annular first surface or the annular abrasive layer, respectively, and into the passive non-grinding central second surface.

According to a preferred embodiment of the invention, the laboratory wheel grinder is designed as an automatic laboratory wheel grinder and has a device head or grinding and polishing head with a piston or pressing shaft for attaching a specimen holder. The piston, to the lower end of which the specimen holder for inserting the specimen or the specimens is attached, is driven by a rotary drive and moved vertically against the grinding disc by means of a linear drive, e.g. a spindle drive. The piston automatically presses the specimens inserted in the specimen holder against the grinding disc with a predefined pressure force in order to effect the grinding process with a defined pressure force, whereby individual pressure or central pressure can be used. In the case of an individual contact pressure, each specimen is pressed individually against the grinding disc by means of a single contact pin and is not fixed in the specimen holder, and is carried along instead, but is axially movable in the specimen holder. In the case of a central contact pressure, the specimens are fixed in the holder, e.g. by means of a radial clamping screw. The rotation of the piston and/or the pressure force against the grinding disc can be preselected by the user by means of a user interface, and the rotation and/or the pressure force caused by the piston is then automatically controlled by a control device. In this process, the grinding is performed under double rotation, namely a rotation of the grinding disc and a rotation of the specimen holder, in opposite directions or in the same direction, which allows for a particularly uniform grinding result.

The specimen holder can be designed, for example, as a disk-shaped holder in which a plurality of specimens is inserted side by side, but it can also be designed as a gripper that grips and holds an individual specimen in particular. Such a gripper as a specimen holder can, for example, be designed as a three-finger gripper.

The laboratory wheel grinder preferably has at least one coolant nozzle for spraying coolant onto the grinding disc. The cooling liquid is then typically collected in the collection tray and can be drained together with the grinding abrasion. In particular, if the laboratory wheel grinder is designed as a combined grinding and polishing device, a plurality of nozzles may be provided in order to be able to additionally apply diamond suspensions of different grit sizes or polycrystalline or monocrystalline grit sizes during the polishing process. Furthermore, both in the manual and in the automatic version, the laboratory wheel grinder may be available either in a single-spindle or a multi-spindle version, i.e. it can comprise one or more grinding stations arranged next to one another, each with a grinding disc mounting plate.

The grinding peripheral annular first surface or the annular abrasive layer has an inner diameter D_i and an outer diameter D_a, with half of the difference between the inner diameter D_i and the outer diameter D_a defining the radial width B_r of the grinding peripheral annular first surface or the annular abrasive layer. This radial width B_r is preferably adapted i) in the case of an individual specimen to the diameter of the specimen or ii) in the case of a plurality of specimen arranged side by side to the diameter of the totality of the specimens. It is preferred in this regard i) in the case of an individual specimen, that the radial width B_r of the grinding peripheral annular first surface is selected in such a way that the diameter of the specimen projects inwardly beyond the inner diameter D_i and/or outwardly beyond the outer diameter D_a, either permanently or temporarily, due to a radial displacement or oscillation of the rotating specimen during the grinding process, and ii) in the case of a specimen holder with a plurality of specimens inserted side by side, that the totality of the specimens relative to the rotation of the specimen holder defines a total outer diameter D_g (circular envelope) and that the radial width B_r of the grinding peripheral annular first surface or of the annular abrasive layer is selected in such a way that the total outer diameter D_g (circular envelope) projects inwardly beyond the inner diameter D_i and/or outwardly beyond the outer diameter D_a, either permanently or temporarily, due to a radial displacement or oscillation of the rotating specimen during the grinding process. This way, in both cases, the specimen or specimens can radially inwardly and/or radially outwardly exceed the grinding peripheral annular first surface or the annular abrasive layer, thus avoiding abrasive regions that do not have any signs of wear. In other words, the grinding disc does not have regions that are covered with abrasive on the one hand but are not exceeded by the specimen or specimens on the other hand, so that there are no abrasive regions on the surface of the grinding disc where the abrasive is not worn by the grinding of the specimen or specimens.

One aspect of the invention also relates to a method for plane grinding the lower side of, in particular, mounted specimens with the rotating grinding disc, in particular with the laboratory wheel grinder described above. In this case, the grinding disc has a carrier disc and abrasive grit bonded to the carrier disc with a bonding agent, or consists thereof, optionally with an intermediate layer, for example made of textile, and is considerably larger than a specimen to be ground. The grinding disc is furthermore divided into a peripheral annular first surface and a central second surface arranged within the peripheral annular first surface, wherein the upper surface of the carrier disc is fully covered with the abrasive grit as abrasive material only in the peripheral annular first surface, so that a grinding peripheral annular first surface or an annular abrasive layer and a passive, non-abrasive central second surface are formed. The one or more specimens are inserted into a specimen holder, which can also be designed as a specimen gripper, and are mechanically pressed against the grinding disc, if necessary. In addition to the rotation of the grinding disc, the specimen holder rotates continuously with the specimen or specimens during the grinding process, and, in the process, an edge region of the specimen or specimens radially extends on the inside and possibly the outside the grinding peripheral annular first surface or the annular abrasive layer into a region without abrasive, in particular permanently or due to the radial oscillation of the specimen holder or the specimen.

In other words, i) in the case of an individual specimen, the specimen defines an outer diameter and the specimen rotates during the grinding process and radially exceeds with its outer diameter the grinding peripheral annular first surface or the annular abrasive layer, respectively, and ii) in the case of a specimen holder with a plurality of specimen inserted, the specimen holder rotates and the totality of the specimens defines a total outer diameter with respect to the rotation of the specimen holder and, during the grinding process. the total outer diameter radially exceeds the grinding peripheral annular first surface or the annular abrasive layer, respectively, to ensure a long-term uniform wear of the abrasive over the entire surface of the grinding disc covered with abrasive.

One aspect of the invention also relates to the grinding disc as a replacement grinding disc comprising a carrier disc and abrasive grit bonded to the carrier disc with a bonding agent as an abrasive, described for the laboratory wheel grinder for the plane grinding of a lower surface of in particular mounted specimens as described above, wherein the grinding disc is substantially larger than the specimen to be ground, wherein the carrier disc of the grinding disc has an upper surface and a lower surface, and wherein the grinding disc is releasably adherable with the lower surface to the grinding disc mounting plate,

-   -   wherein the grinding disc is divided into a peripheral annular         first surface and a central second surface arranged within the         peripheral annular first surface, wherein the upper surface of         the carrier disc is fully covered with the abrasive grit as         abrasive material only in the peripheral annular first surface,         so that a grinding peripheral annular first surface or an         annular abrasive layer and a passive, non-abrasive central         second surface of the carrier disc are formed on the carrier         disc.

One aspect of the invention also relates to the use of the described replacement grinding disc in said laboratory wheel grinder.

Below, the invention will be explained in more detail by means of embodiments and with reference to the figures. In this regard, the same and similar elements are partially provided with the same reference signs and the features of the various embodiments can be combined with each other.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a three-dimensional representation of an embodiment of the laboratory wheel grinder,

FIG. 2 is an enlarged representation of the grinding disc and specimen holder from FIG. 1 ,

FIG. 3 is a cross section through a mounted specimen,

FIG. 4 provides a top view of a grinding disc with the specimen holder from FIG. 2 ,

FIG. 5 is a cross section along the line 5-5 in FIG. 4 ,

FIG. 6 is a detail enlargement of region A from FIG. 5 ,

FIG. 7 is another embodiment of the laboratory wheel grinder,

FIG. 8 is a schematic cross-sectional representation through the specimen holder and grinding disc of FIG. 7 ,

FIG. 9 is a three-dimensional representation through the device head of FIG. 7 without the device head housing,

FIG. 10 is a vertical section through the device head of FIG. 9 ,

FIG. 11 is a cross-sectional representation of the uneven wear of a conventional grinding disc.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1 , the laboratory wheel grinder 10 has a device housing 12, in the present example a an upright housing that is to be placed on a laboratory bench. Above the device housing 12 is a device head 14, in the present example designed as a cantilever arm, which extends over the grinding disc or grinding wheel 16. The grinding disc 16 rotates in a collection pan 18 in the device housing 12. A rotating piston or pressing shaft 20 extends downwardly from the device head 14, and a specimen holder 24, in the present example in the form of a plate, with a connecting pin 26 (FIG. 2 ) is attached to the lower end 22 of the piston 20. In the present example, six mounted metallographic specimens 30 are inserted into the specimen holder 24 or specimen receptacle. The embodiment shown uses a central contact pressure. Alternatively, it is also possible to work with an individual contact pressure, in which case each of the specimens 30 is pressed against the grinding disc with their own pressing stem and is not clamped axially in the specimen holder 24 in a fixed manner (not shown).

The specimen holder 24 and the six mounted specimens or mounted samples 30 inserted therein rotate about the axis of rotation AK of the piston 20 or the connecting pin 26. As a result, the six mounted specimens 30 describe a circular motion about the axis AK and thereby define a total outer circumference 31 with a total outer diameter D_g of about 130 mm in the present example (FIG. 4 ).

In order to grind the specimens 30, the grinding disc 16 now rotates about the grinding disc axis AS on the one hand, and the specimen holder 24 rotates about the axis AK of the piston 20 on the other hand, with the axis AK of rotation of the specimen holder running laterally parallel to the axis AS of rotation of the grinding disc (FIG. 4, 5 ). In particular, the total circumference 31 is outside the grinding disc axis AS, which is advantageous, because the circumferential speed of the grinding disc is zero at its own axis of rotation AS.

There is a contact pressure mechanism, for example with a linear guide 78 (FIG. 9, 10 ) in the exemplary device head 14 with a central contact pressure, which presses the specimen holder 24 with the mounted specimens 30 against the grinding disc 16 in the same direction at a predefined pressing force F during the counter-rotation or rotation of the grinding disc 16 and the specimen holder 24, in order to effect the grinding process of the lower sides 30 a of the specimens by abrasion by means of the abrasive layer of grinding or abrasive grit on the upper side 16 b of the grinding disc.

With reference to FIG. 3 , the specimen 30 is a mounted specimen or embedded sample that consists of the actual specimen material 32 to be examined, e.g. a piece of a metallic test object, e.g. for a later performance of a hardness test or microstructure analyses with a microscope, and a cylindrical block of plastic embedding or mounting material in which the specimen material 32 is embedded or mounted. In particular, the specimen material 32 is mounted in the plastic block 34 to be more manageable. In the present example, the plastic block consists of two different plastics 34 a, 34 b for cost optimization purposes. Bakelite, epoxy resins, thermosets, thermoplastics or acrylic resins for transparent mounting are used as mounting materials, for example.

In FIG. 4 , the grinding disc 16 is divided into a peripheral annular region 42 and a central region 44 arranged in the peripheral annular region. The grinding disc is covered with abrasive material only in the peripheral annular region 44, in the present example with hexagonal abrasive grit. In the central inner region, the abrasive 46 is omitted so that an annular separation line 48 separates the peripheral annular region 42 with abrasive from the central inner region 44 without abrasive. In other words, the abrasive layer 47 is annular in shape and there is no grit in the central inner region 44. The distance between the axes of rotation AK and AS is now selected so that the overall circumferential line 31 of the mounted specimens 30 intersects with the separation line 48 between the peripheral annular region 42 and the central inner region 44, i.e., with the inner diameter D_i of the annular abrasive layer 47. In other words, as the grinding disc 16 and the specimen holder 24 rotate, the mounted specimens 30 travel inwardly beyond the peripheral annular region 42 with abrasive material into the inner region 44 without abrasive material. As a result, there is no location on the grinding disc 16 with abrasive material is not traversed by the mounted specimens 30, thus ensuring a uniform wear of the abrasive material.

The same is true at the outer edge 16 c of the grinding disc 16, because the radial offset between the axes AK and AS is such that the specimens 30 also extend outward beyond the outer edge 16 c of the grinding disc 16.

In the present example, abrasive material 46 is applied to the grinding disc 16 in a hexagonal pattern, although this is not mandatory. Other coating patterns are possible as well. Both the coating pattern and the annular shape of the abrasive layer can be produced in one step by means of screen printing. Using the screen-printing process, the bonding agent with the abrasive grit is printed as a powder on the surface of the grinding disc 16, in the present example directly onto a metal sheet, which forms the rigid carrier wheel 62, so that the abrasive grit is locally mounted in the bonding agent on the grinding disc 16 where desired. However, the carrier disc 62 screen printing may also comprise a textile intermediate layer (not shown) on which the abrasive grit is bonded.

FIGS. 5 and 6 show in even greater detail how the specimen 30, which is currently located on the inside, passes over the peripheral annular region 42 with abrasive material or across the separation line 48 inwards into the inner region 44 of the grinding disc 16 without abrasive material. Due to the fact that the specimen holder 24 rotates in addition to the grinding disc 16, it is nevertheless ensured that all specimens 30 are also ground plane at their periphery 30 c, just not at the very moment when they enter the inner region 44 or the circular lack of abrasive at the center of the annular abrasive layer 47.

In other words, the grinding disc 16 is not completely covered with the abrasive 46 over its entire surface, but only annularly on the outside. Because the specimens 30 always maintain a minimum distance from the axis AS of the grinding disc 16 during the double rotation in the grinding process, a minimum peripheral speed of the abrasive relative to the specimens 30 is maintained in any rotational position. Because the specimens 30 to be ground extend on the inside beyond the peripheral annular region 42 with abrasive, both the abrasive 46 in the peripheral annular region 42 and the lower side 30 a of the specimen 30 are ground plane, eliminating the need to remove the grinding disc 16. This initially saves the user the time required to pull off the specimen. However, as an added benefit, the cost of the abrasive 46 may be reduced as well, because the grinding disc 16 requires less abrasive 46.

If the inner region 44 were also covered with abrasive material, as is typically the case in the prior art, no abrasive material would be removed in the region around the axis of rotation AS of the grinding disc 16, which resulted in a non-planar wear behavior of the grinding disc. Therefore, the grinding disc had to be removed from time to time to make it planar again. Otherwise, uneven wear resulted in a certain transition at a radius r_s of the grinding disc where the overall circumference 31 ends at the center, which meant that the specimens 30 in the edge region 30 c tended to round off during the grinding process and were not plane. FIG. 11 shows this rounding problem 33 as it occurred with traditional grinders or grinding discs.

Returning to the embodiment of the invention shown in FIG. 1-6 , the grinding peripheral annular region 42 has an outer diameter D_a and an inner diameter D_i, in this example the outer diameter D_a=300 mm and the inner diameter D_i=50 mm. These dimensions are adapted to the specimen holder 24 shown in FIG. 4 in the form of a specimen mounting plate, which clamps six mounted specimens 30 in an annular arrangement about the axis AK and which itself has a diameter of 140 mm. In the present example, the specimens 30 have a diameter of 40 mm and the total outer diameter D_g of the overall circumference 31 is approximately D_g=130 mm. The overlapping region or exceeding region 43 of the specimens 30 into the passive inner region 44 is therefore a few millimeters in this example.

However, the principle of the annular configuration of the actively grinding surface 42 of the grinding disc 16 is not limited to specimen holders 24 with a plurality of specimens 30, but can also be used when grinding an individual specimen 30. In this regard, reference is made to FIGS. 7 to 10 , which show a laboratory wheel grinder 10′ having a device head 14 that serves a plurality of grinding stations 15 each with its own grinding disc 16. In this example, the device head 14 is attached to the housing 12 so as to be displaceable along the direction 52 in order to be able to alternately operate a plurality of grinding stations 15. Each grinding disc 16 rotates in its own collection tray 18 in this example. The laboratory plate grinder 10′ also has two separate polishing stations 54.

In FIG. 8 , each grinding station 15 has a grinding disc mounting plate 58, which may be formed, for example, as a stable metal plate. The grinding disc mounting plate 58 is rotated about the axis AS by a grinding disc drive 60. The grinding disc 16 is detachably adhered to the grinding disc mounting plate 58, for example by means of a magnetic holder, although other adhesion techniques are possible as well.

The grinding disc 16, in turn, has a stiff carrier disc 62 and the abrasive material 46 bonded to the carrier disc 62 in the form of abrasive grit of a specific grit size mounted in the bonding agent, thereby forming the abrasive layer 47. In this case, the abrasive grit is applied to the carrier disc in multiple layers to form a self-sharpening grinding disc 16. For this purpose, the abrasive grit is printed as a powder onto the grinding disc 16, in this example directly onto the upper surface 62 b of the carrier disc 62, for example by means of a screen-printing process with a synthetic resin bonding agent. Depending on the grit size, this means that approximately 3 to 100 layers of abrasive grit may be bound in the bonding agent on the carrier disc 62. The thickness of the abrasive layer 47 thus produced is about 0.2 mm to 1 mm, depending on the grinding disc 16. By means of the screen-printing process, a desired abrasive pattern, e.g. hexagonal, as shown in FIG. 2 , and the separation into the peripheral annular region 42 with abrasive and the inner region 44 without abrasive can be produced in one step. As a result of the separation into the peripheral annular region 42 with abrasive material and the inner region 44 without abrasive material, a step 64 is formed at the annular separation line 48 between the peripheral annular region 42 with abrasive material and the inner region 44 without abrasive material, the height of said step corresponding to the thickness of the abrasive material layer 47, i.e. is, for example, approximately 0.2 mm to 1 mm. The step 64, which runs downward from the peripheral annular region 42 into the inner region 44, ensures that even if the abrasive 46 in the peripheral annular region 42 is significantly worn, the specimen 30 still has a sufficient axial distance from the upper surface 62 b of the carrier disc 62 and, in particular, that no undesirable step can occur upward from the peripheral annular region 42 into the inner region 44, as is the case with conventional grinding discs when the abrasive in the central region of the grinding disc is not worn off by the specimen or specimens. Therefore, a regular removal in order to render the grinding disc plane again can be dispensed with. The lower surface 62 a of the carrier disc 62 is adhered to the upper surface 58 b of the grinding disc mounting plate 58.

In the example shown in FIGS. 7 to 10 , the specimen holder 24 is configured as a specimen gripper 72. The specimen gripper 72 has three gripper arms 74 which can automatically grip an individual specimen for automatic grinding. By means of a plurality of nozzles 76, for example, water can be automatically sprayed onto the grinding disc 16 as a coolant and/or for rinsing purposes, or diamond suspensions in various grit sizes.

Referring to FIGS. 9 and 10 , the device head 14 has a linear drive mechanism 78 by means of which the specimen holder 24 and thus the specimen 30 or specimens 30 are applied against the grinding disc 16 with a defined force F, with the piston 20 rotating at the same time.

It is apparent to a person skilled in the art that the embodiments described above are to be understood as exemplary and that the invention is not limited to these, but can be varied in a number of ways without departing from the scope of protection of the claims. Furthermore, it is apparent that the features, whether they are disclosed in the description, the claims, the figures or otherwise, also individually define essential components of the invention, even if they are described together with other features. All features disclosed in connection with the laboratory wheel grinder, the method, the replacement grinding disc and the use are, of course, also considered disclosed for the objects of the respective other categories, and the features of one embodiment are also considered disclosed for another embodiment. In the present case, this applies in particular to the two embodiments in FIG. 1-6 on the one hand and FIG. 7-10 on the other. 

1. Laboratory wheel grinder with a rotating grinding disc for the plane grinding of a lower side of mounted specimens, comprising: a device housing with a grinding disc mounting plate and a drive motor, by means of which the grinding disc mounting plate can be set in rotation, a grinding disc having a carrier disc and an abrasive bonded with a bonding agent on an upper surface of the carrier disc, wherein the carrier disc of the grinding disc has an upper surface and a lower surface, and wherein the lower surface of the grinding disc can be detachably mounted on the grinding disc mounting plate, wherein the grinding disc is divided into a peripheral annular first surface and a central second surface disposed within the peripheral annular first surface, wherein the upper surface of the carrier disc is coated with the bonded abrasive only in the peripheral annular first surface to form a grinding peripheral annular first surface and a passive central second surface.
 2. Laboratory wheel grinder according to claim 1, wherein the abrasive means are formed by abrasive grit and, in the cross section of the grinding disc, the abrasive grit in the grinding peripheral annular first surface defines a common annular abrasive first surface of the grinding disc and the carrier disc of the grinding disc in the passive central second surface forms a central non-abrasive second surface of the grinding disc, and wherein, in a fresh unused condition of the grinding disc, the common annular grinding first surface of the grinding disc is higher than the central non-grinding second surface of the grinding disc.
 3. Laboratory wheel grinder according to claim 2, wherein the difference in height between the common annular abrasive first surface and the central non-abrasive second surface ranges from 50 μm to 5 mm.
 4. Laboratory wheel grinder according to claim 1, wherein the abrasive is formed by abrasive grit and, in the grinding peripheral annular first surface, the abrasive grit is bonded with the bonding agent in a plurality of layers, on the upper surface of the carrier disc.
 5. Laboratory wheel grinder according to claim 4, wherein the abrasive layer is multi-layered and is self-sharpening in such a way that dull abrasive grit breaks out during the grinding process and fresh abrasive grit, emerges from an underlying layer to the surface.
 6. Laboratory wheel grinder according to claim 1, wherein the abrasive is formed by abrasive grit and, in the grinding peripheral annular first surface, is printed with a bonding agent in a predefined pattern.
 7. Laboratory wheel grinder according to claim 1, wherein the grinding disc is round and/or has an outer diameter of between 100 mm and 500 mm.
 8. Laboratory wheel grinder according to claim 1, wherein the grinding peripheral annular first surface has an inner diameter D_i and an outer diameter D_a, wherein half of the difference between the inner diameter D_i and the outer diameter D_a corresponds to the radial width B_r of the grinding peripheral annular first surface and is between 240 mm and 20 mm.
 9. Laboratory wheel grinder according to claim 1, wherein the grinding peripheral annular first surface has an inner diameter D_i and an outer diameter D_a, wherein the inner diameter D_i has a range of between 20 mm and 450 mm, and the outer diameter D_a has a range of between 100 mm and 500 mm.
 10. Laboratory wheel grinder according to claim 1, wherein the carrier disc comprises a metal sheet or a plastic sheet, and/or wherein the abrasive consists of diamond particles.
 11. Laboratory wheel grinder according to claim 1, wherein the grinding disc can be fastened with the lower side on the grinding disc mounting in a removably adhering manner.
 12. Laboratory wheel grinder according to claim 1, wherein the device housing comprises a collection tray for cooling liquid and grinding abrasion, with the grinding disc mounting plate rotating in the collection tray.
 13. Laboratory wheel grinder according to claim 1, wherein one or more specimens are inserted into a specimen holder and pressed against the grinding disc, and wherein, in addition to the rotation of the grinding disc, the specimen holder rotates with the specimen or specimens during the grinding operation, and an edge region of the specimen or specimens extends radially inward beyond the grinding peripheral annular first surface during the rotation of the grinding disc and the specimen holder.
 14. Laboratory wheel grinder according to claim 1, wherein the laboratory wheel grinder comprises a device head with a piston for fastening a specimen holder, with which one or more specimens inserted in the specimen holder are pressed onto the grinding disc with a predefined pressure force, and wherein the specimen holder is rotatable in order to simultaneously bring about a rotation of the specimen holder during the grinding process in addition to the rotation of the grinding disc, wherein the axes of rotation the grinding disc and of the specimen holder extend in a parallel offset manner.
 15. Laboratory wheel grinder according to claim 1, wherein the grinding peripheral annular first surface has an inner diameter D_i and an outer diameter D_a, and wherein half of the difference between the inner diameter D_i and the outer diameter D_a defines the radial width B_r of the grinding peripheral annular first surface, and i) in the case of an individual specimen, the radial width B_r of the grinding peripheral annular first surface is selected such that the diameter of the specimen protrudes internally beyond the inner diameter D_i, due to a radial displacement of the rotating specimen during the grinding process, or ii) in the case of a specimen holder with a plurality of inserted specimens, the totality of the specimens defines an overall outer diameter D_g relative to the rotation of the specimen holder, and the radial width B_r of the grinding peripheral annular first surface is selected such that the overall outer diameter D_g projects internally beyond the inner diameter D_i, due to a radial displacement of the rotating specimen during the grinding operation.
 16. Method for the plane grinding of a lower side of mounted specimens with a rotating grinding disc or with the laboratory wheel grinder wherein: a grinding disc having a carrier disc and an abrasive bonded with a bonding agent on an upper surface of the carrier disc is used, and wherein the carrier disc of the grinding disc has an upper surface and a lower surface, wherein the grinding disc is larger than the specimen to be ground, wherein the grinding disc is divided into a peripheral annular first surface and a central second surface arranged within the peripheral annular first surface, the upper surface of the carrier disc being covered with the abrasive only in the peripheral annular first surface so as to form a grinding peripheral annular first surface and a passive central second surface, wherein one or more specimens are inserted into a specimen holder and pressed against the grinding disc, and wherein, in addition to the rotation of the grinding disc, the specimen holder rotates with the specimen or specimens during the grinding operation and, during the rotation during the grinding operation, edge portions of the specimen or specimens extend inwardly beyond the grinding peripheral annular first surface and into the passive central second surface.
 17. Replacement grinding disc consisting of a carrier disc and abrasive grit bonded to the carrier disc with a bonding agent, prepared for use in the laboratory wheel grinder for the plane grinding of a lower side of mounted specimens according to claim 1, wherein the grinding disc considerably larger than the specimen to be plane-ground, wherein the carrier disc of the grinding disc has an upper side and a lower side, and wherein the carrier disc can be detachably adhered with the lower side to a grinding disc mounting plate of the laboratory wheel grinder, and wherein the grinding disc is divided into a peripheral annular first surface and a central second surface arranged within the peripheral annular first surface, wherein the upper surface of the carrier disc is coated with the abrasive grit as abrasive only in the peripheral annular first surface, so that a grinding peripheral annular first surface and a passive central second surface are formed.
 18. Use of the replacement grinding disc according to claim 17 in the laboratory wheel grinder according to claim
 1. 